|Tidal Zone||Marine Offshore Subtidal
|Definition||The Marine Offshore Subsystem extends from the 30 meter depth contour to the continental
shelf break, as defined by the maximum slope discontinuity with a rapid change in
gradient of 3° or greater at the outer edge of the continental shelf. This shelf break
boundary generally occurs between 100 - 200 meters depth. In the case of steep-sided,
oceanic islands, where a continental shelf is not present, the offshore boundary of
the Offshore Subsystem is defined at a bottom slope discontinuity occurring between
100 - 200 meters, or at 200 meters if no such discontinuity exists.
The waters and benthos of the Offshore Subsystem are less coupled to each other and typically less influenced by terrigenous processes than in the Nearshore Subsystem. Distance from shore can vary greatly, depending on shelf morphology, and waters at the 30 meter isobath can be quite distant from the shore or may lie relatively close to land.
The Offshore Subsystem may be strongly influenced by open-ocean biogeochemistry and physical processes. Often distinct water layers at the surface and bottom may be present. Because Offshore Subsystem waters are less influenced by coastal inputs, they generally are less turbid than those of the Nearshore Subsystem. Light penetration in the Offshore Subsystem can extend to significant depths and often reach the ocean bottom.